In known enclosures for receiving and housing electronic modules or cards containing electronic components, the RFI/EMI emissions are contained by enveloping the enclosure in a sheet metal shroud and plating the plastic components of the housing. The sheet metal shroud typically has a plurality of small holes for ventilation and either completely covers the enclosure or at least covers substantial portions of the enclosure. This sheet metal shroud is effective in preventing RFI/EMI emissions from the electronic components but adds substantial weight to the overall enclosure. In addition, if aluminum foil is used instead of sheet metal, the overall material cost is increased.
Known enclosures that provide the necessary Faraday shield through the use of sheet metal typically have a plurality of small holes for ventilation, typically, one-eighth of an inch in a material with the thickness of approximately one-sixteenth inch. Any large openings to permit air flow also permit the release of RFI/EMI emissions. Known enclosures use fans to move air through these small openings to dissipate the heat generated by the electrical components. However, in order to adequately cool such known systems, the volume of air flow through the relatively small apertures create an air turbulence noise. When the enclosure is placed in an otherwise quiet work environment, the air flow noise is a source of irritation and distraction to workers in the area.
In a typical enclosure, the electronic modules or cards are inserted into guides or channels which orient the modules or cards within the enclosure. The frequent removal and reinsertion of the modules or cards within the guides of the enclosure cause wear to the surface of the guides. The wear of the guides results in the release of small particles of conductive material which can settle on the modules or cards and cause damage to sensitive electronic components and connections. Furthermore, the removal of material from the guides can create a hole in the Faraday shield and the leakage of emissions.
When a module or card is inserted into the enclosure, electrostatic discharge (ESD) resulting from a static electric charge build-up on the module or card can be transferred throughout the entire system, causing damage to sensitive components. In order to eliminate damage to system components from ESD, known methods include static pads that the operator stands on during assembly and various sprays to remove static electricity. These methods are relatively ineffective and require operator cooperation. The specification for the IEEE Futurebus, which is defined by IEEE P896.2, requires some form of positive discharge of static electricity between the module or card and the enclosure. Of course, the Futurebus specification and other relevant specifications, such as the IEEE Standard for a Metric Equipment Practice for Microcomputers Coordination (IEEE P1301) do not prescribe any physical structure to achieve the desired static discharge.
In known enclosures, the modules or cards if withdrawn while power is present can cause a power surge resulting in damage to other modules or cards or a disruption in their operation. If a module or card is inserted into an enclosure that has power being supplied to other modules or cards, damage because of high current inrush is possible. In order to prevent the withdrawal of modules or cards, various electronic circuits or mechanical locking devices have been developed. The complexity of the mechanical locking devices increases the cost of materials and assembly of the enclosure.